The present invention relates to a combustion system and particularly to an improved system for fusing a solid or liquid specimen into a gaseous sample for subsequent analysis.
There exists a variety of combustion systems for the combustion of analytical samples to determine, for example, the sulphur content of coal, coke or other substances. The sulphur level can be determined from a solid or liquid specimen which is positioned in an induction furnace and combusted to provide a gaseous sample. The gaseous sample is subsequently drawn from the combustion chamber and analyzed by an infrared or other detector for detecting the sulphur dioxide concentration which is then displayed by a digital display as the sulphur content of the specimen. Certain aspects of previous combustion systems used in such analyzers is disclosed in U.S. Pat. No. 3,923,464 issued 12/2/75 to Sitek et al and assigned to the present assignee.
Such systems are open ended and employ a carrier gas introduced into the combustion chamber of the induction furnace to oxidize the specimen and carry the resultant gas through the opposite end of the combustion chamber and to an infrared cell for detection. A closed loop combustion system of this general type is also described in U.S. Pat. No. 3,985,505 issued 10/12/76 to R.L. Bredeweg, and assigned to the present assignee.
Although these systems provide excellent results in analyzing certain specimens, coal cannot be heated directly with radio frequency energy used in these systems since it is a non-conductor. As a result, accelerating agents, such as iron chips or powder, or tungsten, are required to be added to the sample. Further, the combustion chamber in such systems is relatively small and due to the fact that the coal is naturally combustible and creates an exothermic reaction during its combustion, it tends to sputter and some of the specimen can easily escape from the hot zone of the combustion chamber and not be broken down to provide an accurate analysis.
U.S. Pat. No. 4,282,183 issued 8/4/81 to R.L. Bredeweg et al and assigned to the present assignee and U.S. Pat. No. 4,352,781 issued 10/5/82 to O'Brien and also assigned to the present assignee, disclose improved combustion chambers having relatively large hot zones and an open end for receiving a combustion boat containing the specimen to be analyzed and an enclosed opposite end. The specimen gas is withdrawn from near the closed end of the combustion chamber by an eduction tube extending within the combustion chamber. The open end of the chamber is effectively sealed by a gas curtain such that the interior of the chamber is available to the operator for readily inserting and removing specimens for combustion. The combustion system represented by these patents, provide improved results, however, they utilize a significant number of ceramic and quartz parts which must be carefully aligned and attached to one another to maintain their interrelationship for most effective operation. Thus several of the parts are cemented using a refractory cement which can break during use due in part to thermal expansion and contraction. Also, in these combustion systems, the gases pass relatively quickly through the combustion zone and are withdrawn either externally to the combustion chamber or through an eduction tube having a relatively small diameter within the combustion chamber. As a result, if the size of the combustion is too large, incomplete combustion may result in inaccurate measured specimen concentration.